Telephone-exchange system



n. M. TAG'G-ART.

TELEPHONE EXCHANGE SYSTEM. AIPPLICATION FILED DEC.28. 1918.

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DA ES-ON M. TAGGART, OF EAST ORANGEfNEVI' JERSEY, ASSIGNOR TO WESTERN ELEGTRIC COMPANY, INGOREORAT'ED, OF NEW YORK, N. Y., A. CORPORATION OF NEVI YORK.

TELEPHONE-EXCHANGE SYSTEM.

Patented Oct. 19, 1920.

Application filed December 28,1918. Serial No. 268,625.

To all whom it may concern Be it known that l, DAWSGN M. TAGGART, a citizen or the United States, residing at East Orange, in the county of Essex, State 01" New Jersey, have invented certain new and useful Improvements in Telephone-EX- change Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone eX- change systems and more particularly to such systems in which connections are to be established between telephone lines terminating at a manual exchange and telephone lines terminating at an automatic ex change. 7 r

In such systems it is frequently the practice to employ trunk circuits which areaccessible to selecting apparatusatthe automatic exchange so that a call from a subscriber whose line-terminates thereat may be extended to the manual exchange.

In systemsot this nature it is desirable to provide means whereby the restoration of the receiver at the subscribers station associated with the automatic exchange will im' mediately release the selecting apparatus of the automatic exchange which may he associated with the trunk during the connection. it is the object of the invention to provide an improved signaling system in a trunk uit of: this nature interconnecting eX- changes of this character.

To attain this object in accordance with a eature oi the invention, means is provided ciated with a trunk circuit of this na :0 for momentarily varying the resistance circuit with the releasing means of the selector upon the termination of the converration hy the suoscriber whose line termiu the automatic exchange, whereby rough the selectors associated with the re immediately released, a busyconion of the trunk terminals is tlierear'ter restored and is maintained until disconnection from the trunk is effected at the manual exchange. g

This and other features of the invention, not specifically mentioned above, will clearly appear from the following specification and the an exed drawing in which the figure shows ..iagrammatically one embodiment of the invention applied to a trunk circuit interco 'uiecting manual and automatic exchange.

shown as terminating atan automatic ex- 7 7 change It and adapted to be connected to the trunk circu1t C extending to the manual ex hange Y, by means of a selecting means B which may be of a step-by-step type involving known CllCllltS, only sufficient por-.

tions thereof being shown to properly illus trate the inventlon. A. cord circuit D of any usual type is provided at the manual 1 right of such line is located at the manual exchange. it

It is thought that the nature of the invention may be more fully comprehended from the following description of the operation of the system shown inthe drawing.

Assuming that the subscriber associated with the line circuit A. terminating atexchange or central ofiice X, desires to'con verse with a subscriber whose line (not shown) terminates at the exchange or central oflice Y, and by removing the receiver has obtained connection with the selecting circuit B by mea'nsof a line switch or by any other suitable means. comprises in part a line relay 1, a slowrele'aserelay 2, a release magnet 3, an OK- normal contact i, a cut-ofii relay 5, a switch arm 6, terminals 7, 8 and 9' for cooperation therewith, and wipers 10,11 and 12 for extending the calling 'line to the selected trunk circuit. Upon the connection of the calling line with the selector B, relay 1 0p crates over a circuit established from bat tery, through the leilt hand winding of relay 1, the middle normal contact of relay 5, one conductor, of the line circuit A, through the sub-station apparatus; associated with such line, returning over the other conductor of the line, the upper norrelease relay 2 remaining operated during process, and the off-normal contact 4 closing at the first movement of the selector.

The selector B T through the wipers 10 and 11, and at its lower normal contact opening the lead connected to the off-normal contact 4;. Thereupon trunk line relay 14 operates over a circuit established from battery, through the right-hand winding of relay 1 1, the conductor of trunk circuit C connected with the wiper 11, the lower alternate contact of relay 5, the ring conductor of the line cir cuit A, the sub-station apparatus associated with such line, the tip conductor of the line,

the upper alternate contact of relay 5,-the wiper 10 and the conductor of the trunk circuit associated therewith, and the left-hand winding of relay 14, to ground. Slow-release relay 15 operates over a circuit established from battery, through the winding of relay 15 and the contact of relay 14:, to ground, and causes the operation of control relay 16 over a circuit established from battery, through the winding of relay 16 and the contact of relay 15, to ground. The closure of'the outer left-hand contact of relay 16 connects ground to the release trunk lead or control conductor 30' connected with the wiper 12, thereby establishing the usual busy condition of the test contact associated with the trunk circuit C. Relay 1 releases 7 upon the opening of the upper and middle normal contacts of relay 5. Relay 2 thereupon releases to open the operating circuit of' relay 5 andto prepare a circuit for the release magnet 8, but due to the slow release nature of relay 2, relay 16 operates prior to the complete release of relay 2; Therefore,v

relay 5 is maintained operated over a circuit established vfrom battery, through the terminal 9, the switch arm 6, the winding of relay 5, the wiper 12 and the release trunk conductor in contact therewith, and the outer left-hand contact of relay 16, to ground. The closure of the inner left-hand contact of relay 16 operates slow release control relay 17 over a circuit extending from battery, through the right-hand winding of relay 17 and the inner left-hand contact ofrelay 16, to ground. The closure of the outer right-hand contact of relay 16 shortcircuits the high resistance left-hand winding of relay 18 which is included with the low resistance right-hand winding of such relay and the retardation coil 19 in a bridge across the tip and ring conductors of the trunk circuit. The closure of the inner right-hand contact of relay 16 operates'relay 20 over a circuit established from battery, through the winding of relay-20, the

contact of relay 21, the tip conductor'of the trunk circuit C, the inner right-hand contact of relay 16 and the normal contact of relay 18, to ground. Lamp 22 is there upon lighted over a circuit extending from battery, through the contact of relay 20 and the lamp 22 to ground.

Upon observing the illumination of the lamp 22, the operator-at exchange Y inserts plug 23 of cord circuit D into jack 24; of 1 the trunk circuit C. The resistance of the bridge, including the retardation coil 19 and "the right-hand winding of relay 1,8, is such that the supervisory relay 25 and trunk relay 18 are operated over a circuit extending .from battery, through the winding of relay 7 i '23 and jack 2 1, and the winding of relay 21, to ground. Resistance'27 shunts lamp 26, thereby, in the usual manner, preventing the lighting of such lamp, and relay 21 opcrates to release relay 20, thereby extinguishing. calling lamp 22. The actuation-of the usual listeningkey 29 enables the operator at the exchange Y to converse with the calling subscriber, and after the number of the desired line is ascertained, the trunk circuit C may'be connected to such called line (not shown) in the usual manner.

Upon the termination of the conversation, the subscriber associated with the line A in replacing the receiver releases relay-14c.

which in turn releases relays 15, 16 and 17:

After'the release of relay 16 and beforeslow release relay 17 has completely released in response thereto, a circuit is momentarily established from battery, through the terminal 9, the switch arm 6, the winding of relay .5, the wiper 12 and the release con- 3 ductor '30 of the trunk connected therewith, thehighresistance left-hand winding of relay 17 and the alternate contact'of relay 18 to ground. The resistance of the left-hand winding of relay'17 is of suflicient value to cause the release of relay' 5, thereby interrupting.thewcontinuity of the tip and ring conductors, reconnectingthe line relay 1 to the selector and completing a circuit for the release magnet 3 extending from battery, through the 'WlIlCllIlg of the release magnet 3,.the oif-normalicontact 4 (now closed) the lower contact of -relay-5, the normal contact of relay 2, and the normalcontact of relay 1 to ground. Thereupon the selector B is disconnected from the trunk circuit C and is restored to normal condition in theusual manner. However, the complete release of relay 17 short-circuits the high resistance left-hand winding thereof,thereby connecting the usua busy ground potential to the testing terminal of the trunk circuit at the automatic exchange through the alternate contact of relay-18 and the normalycontact of relay 7, trunk against selection by any selector. Thus through the coopera'ion of the trunk line relay 14:, slow release relay 15, control relay l6 and slow-release control relay 17, the restoration of the receiver to the switchhool: at the station on line A, reduces the resistance of the control conductor 30 sufliciently to cause the release of the automatic switching apparatus by means of which such lin is connected with the trunk C, but a grounding potential is maintained to prevent the reselectionof such trunk.

T he opening of the outer right-hand contact of relay 16 removes the short circuit established around the left-hand high resistance winding of relay 18, whereupon the resistance of the bridge across the trunk conductors is increased sufliciently to cause the release of supervisory relay 25 in the cord circuit 13 to light lamp 26 over a circuit established from battery, through the lamp 26, the resistance 28, the sleeve contacts of plug 23 and jack 24, and the windof relay 21 to ground. The subsequent removal. of plug 23 from ack 24 responsive to the disconnect signal restores all apparatus to normal.

It will be evident that with this invention the possibility of the selector being unavailable for future use during the interval between the termination of the conversation by the subscriber whose line terminates at the automatic exchange and the disconnection from the trunk circuit by the operator at the manual exchange, is eliminated without rendering the trunk circuit C selectable by other selectors during that period.

What is claimed is:

1. A telephone exchange system comprising a trunk circuit including a normally op n control conductor terminating at a central office, line circuit terminating at the otfice, a source of current, switching means controlled over the conductor for establishing connection between the line and trunk circuits for closing the control conductor and for connecting the source of our i t thereto, a link circuit at another central for connection with the trunk cirwit. and means responsive to the opening of the line circuit for reducing the current flow in the control conductor to a predetermined positive value.

thus effectively guarding the 2. A telephone exchange system comprising a trunk circuit including a normally open control conductor extending from a first to a second central office, a telephone line at the first o'flice, a source of current, switching means controlled overthe conductor for establishing connection between the line and the trunk circuit for closing the control conductor and for connecting the source of current thereto, a link circuit at the second central office for connection with the'trunk circuit, means responsive to the opening of the telephone line for reducing the current flow in the control conductor to a predetermined positive value, and means responsive thereto for releasing the switch ing means to disconnect the line from the trunk circuit. Y

3..A telephone exchange system comprising a trunk circuit including a normally open control conductor extending from a first to a second central ofiice, a telephone line at the first oflice, a source of current, switching means controlled over the conductor for establishing connection between the line and the trunk circuit and for closing the control conductor and for connecting the source of current thereto, a link circuit at. the second central office for connection with the trunk circuit, and means readapted to be connected to ground upon connection of the line with the trunk circuit, a link circuit at the second central oflice for connection with the trunk circuit, and means controlled by the contemporaneous connection of the link circuit and the line with the trunk circuit to maintain the ground connection of the test terminal independently of the continuance of the 'connection between the line and the trunk circuit. I

5. A telephoneexchange system comprising a trunk circuit including a normally open control conductor extending from a first to a second central office, a telephone line at the first office, a source of current, switching means controlled over the conductor for establishing connection between the line and the trunk circuit and for closing the control conductor, a link circuit at the second central oiiice for connection with the trunk circuit, means responsive to the opening of the line for momentarily reducing the current flow inthe control conductor to a predetermined positive value, and

&

means responsive thereto for releasing the switching means to disconnect the line from the trunk circuit.

6. YA telephone exchange system comprising atrunk circuit including a normally open control conductor extending from a first to a second central oflice, a telephone line at the first oflice, a source of current, switching means controlled over "the conductor for establishing connection between the line and the trunk circuit for closing the control conductor, and for connecting the source of current thereto, a link circuit at the second central oi'lice for connection with the trunk circuit, and a signaling device in the link circuit responsive to a reduced ourrent flow in thecontrol conductor. 7

7. A telephone exchange system comprising a trunk circuit including a normally open control conductor extending from a first to a second central office, a telephone line at the first office, a source of current,

switching means controlled over the conductor for establishing connection between the line-and the trunk circuit and for closing the control conductor, a link circuit at the second Office for connection with the trunk, a signaling device associated with the line from the trunk circuit and for operating the signaling device.

In witness whereof I hereunto subscribe my name this'27th day of December, A. D.,

DAWSON M. TAGGART. 

